Set of metamorphic mineral assemblages, repeatedly associated with each other in space and time.

There is a predictable and common correspondence between the mineralogy of each rock and its bulk chemical composition.

The mineral assemblage defining the metamorphic facies indicates that a state of stable equilibrium has been attained over a restricted P-T condition.

Several different facies have been formally recognized and have names referring to distinct aspects of the facies.

• e.g. green schist facies = characterized by schists in which green chlorite, talc, serpentine, epidote and actinolite are predominant.

Mineralogical characteristics of the metamorphic facies corresponding to those on the Handout - Facies vs. Grade are:

1. Zeolite Facies
   • Zeolites are groups of white to colourless hydrous alumina silicates, analogous in composition to feldspars.
   • Laumontite, heulandite and analcine are common, the assemblage Quartz + Laumontite + Chlorite is diagnostic.
2. Prehnite - Pumpellyite
   • Prehnite +/- Pumpellyite + Quartz is typical.
   • Prehnite - Ca₂Al₂Si₃O₁₀(OH)₂ Pumpellyite - Ca₂MgAl₂(SiO₄)(Si₂O₇)(OH)₂H₂O
3. Glaucophane - Lawsonite Schist or Blueschist
   
   • High P Low T
   • Glaucophane (Na₂MgAl₂Si₈O₂₂(OH)₂) (alkali-rich amphibole) + Lawsonite (CaAl₂Si₂O₇(OH)₂H₂O) are characteristic
     also
   • Jadiete (NaAlSi₂O₆) + Qtz + Aragonite
4. Greenschist
   • Albite + Epidote + Actinolite + Chlorite + Calcite in mafic rocks
   • pyrophyllite in pelitic rocks
5. Amphibolite
   • Hornblende + Plagioclase (An > 20)
   • Kyanite (Al₂SiO₅) in pelites
6. Granulite
   
   • lower crustal lithology
   • cpx + opx + plag + Fe - Mg garnet
7. Eclogite
   • lower crust or upper mantle lithology
   • Feldspar-free assemblages, with jadiete-rich cpx + pyrope (Mg-rich garnet)

The pressure and temperature range for each facies given in Handout - Facies vs. Grade. The assemblages listed above are mainly for mafic (Metabasite) lithologies. Boundaries between individual facies are not sharp, marked by reactions which occur over a P-T range depending on composition.